The use of segmented mechanical couplings for joining and sealing the ends of pipes has attained wide commercial acceptance, and these couplings are now employed in many industries. A typical segmented coupling is disclosed in U.S. Pat. No. 3,054,629, to Piatek, issued Sept. 18, 1962. The coupling includes a pair of arcuate coupling segments which span and embrace the adjacent ends of a pair of pipes, and which compress a sealing gasket into engagement with the external periphery at the end of pipes, (hereinafter referred to as the pipe ends). The coupling segments have keys on their inner periphery for engagement within grooves in the adjacent pipe ends, and having radially extending pads at their ends which receive bolts employed for tightening down the coupling. The keys alternatively may be engaged with external beads rolled in the pipe ends.
Optimally, when the segments are secured together, they extend in a continuous ring about the circumference of the pipe ends and substantially immobilize the pipe ends and eliminate all gaps between the segments. However, differences in the diameter of stock pipe of the same nominal diameter result in a less than optimal immobilization of the pipe ends, or gaps which permit extrusion of the contained gasket. Similar problems arise due to differences in the depth of the groove on the pipe ends. If the pipes are undersized in diameter, or the groove diameter is too small then, the bolting pads may be brought into face engagement with each other, but, the desired immobilizing clamping force on the pipe ends may not be obtained. If the pipes are oversized in diameter, or the groove diameter is too large, then the bolting pads may not be brought into face engagement with each other and may leave a gap between the bolting pads through which the gasket can extrude. To overcome these problems, relatively closely spaced apart supports or hangers have been employed to eliminate undesirable flexure at the joint, or extrusion shields have been provided to support the gaskets in the area of the gap between the bolting pads.
At least one approach to solving the first problem, that is, flexure at the joint, is addressed in Gibb et. al., U.S. patent application Ser. No. 358,361, filed Mar. 15, 1982, now Pat. No. 4,471,979, as applied to thin-walled piping which is inherently capable of moving out-of-round under compressive stresses produced by the tightening down of the coupling. Gibb et. al. teach the deliberate formation of the coupling segments for them to subtend an angle of less than 180 degress at their end faces, to permit the centers of curvature of the respective coupling segments to move beyond and to opposite sides of the diametral plane of the coupling. This selective deformation of the pipe ends by the coupling provides for rigid clamping of the coupling onto the pipe ends without regard to whether the pipes are oversized or undersized within the range of manufacturing tolerances. This construction, however, is of little utility for use with conventional pipe that is not readily deformable by a coupling, and does not eliminate the need for extrusion shields in those instances where the bolting pads do not reach face engagement with each.
U.S. Pat. No. 2,752,173, to Kroos, teaches flexure of the coupling segments to move the ends thereof in a radially inward direction for them to clamp onto pipes of less than maximum diameter within the range of manufacturing tolerances. While this will produce clamping in the diametral plane of the end faces, flexure of the coupling segments in Kroos will produce an increase in the effective length of the inner periphery of the coupling and preclude clamping of the coupling onto the pipes other than at the ends of the coupling segments. Further, in Kroos, flexure of the coupling segments results in movement of the end faces away from each other and increases the possibility of gasket extrusion.